In order to explore the swelling deformation and calculation model of expansive soil, taking the expansive soil in Ankang area of Shaanxi Province as the research object, we carried out a series of indoor tests, which are non-loaded expansion rate tests and expansion force tests with different dry densities and different initial moisture contents, as well as loaded expansion rate tests under the same dry densities. Based on the test results, the calculation model of expansion rate was improved considering the factors of initial moisture content, initial dry weight and overburden load. The test results show that the expansion of Ankang expansive soil decreases with the increase of initial moisture content, the decrease of initial dry density and the increase of overburden pressure. The relationship curves between non-loaded expansion rate and time of expansive soil fits in the Logistic model, and each can be divided into three stages according to different expansion rates. The expansion force decreases with the increase of initial moisture content and the decrease of dry density. In addition, the expansion force remains small and changes little under low dry density (ρd<1.47g/cm3). The improved calculation formula considering three factors is correct, which can provide reference for the prediction of Ankang expansive deformation and engineering construction.